The present invention relates to a planetary-transmission comprising a sun gear, which constitutes an input drive means to the planetary transmission, a ring gear arranged around the sun gear, a planet carrier which is designed to rotate and which carries at least one planet wheel, which planet wheel meshes with the sun gear and the ring gear. The planet carrier constitutes an output drive means from the planetary transmission. The planetary transmission further comprises a wet disk brake, a first set of brake disks in the brake being rotationally locked to the planet carrier and thereby in operation rotating at the rotational speed of the planet carrier. The invention further relates to a drive device comprising such a planetary transmission.
The invention relates primarily to the field of work machinery or work vehicles, such as wheel loaders and dumpers (frame-steered vehicles). The invention could also be utilized for other types of work vehicle, such as backhoes (excavator loaders), and excavators. The invention also has applications in other types of heavy, non-commercial vehicles, such as trucks.
The drive device therefore comprises the planetary transmission and forms a so-called final drive, or hub-mounted reduction gear. The wheel is then arranged rotationally locked on a hub and the planetary transmission is connected between a drive shaft and the hub. The drive shaft is driven by an angular gear, or center gear, which is in turn driven by the vehicle engine by way of a transmission system.
Arranging a planetary transmission on each drive wheel in this way produces a reduction in rotational speed from the drive shaft to the hub and an increase in torque from the drive shaft to the hub.
Since the planet carrier is rotationally locked to the wheel hub the first set of brake disks will in operation rotate at the speed of the wheel. Such a brake affords a high degree of precision and sensitivity in braking.
Rotationally locking a first set of brake disks to a planet carrier in such a planetary transmission, as disclosed by WO 99/03699, for example, is already known. The brake disks are then connected via splines on a radially outer surface of the planet carrier.
WO 04/104436 describes a planetary transmission in which multiple planet wheel journals are joined by a bolted connection to a common, annular carrier, which has radially outer splines for the first set of brake disks.
It is desirable to provide a planetary transmission with an integral brake, which affords a good circulation of cooling fluid to the brake. The invention is also intended to minimize the number of parts and/or to provide a design construction that is as simple and hence as cost-effective as possible. A further intention is to achieve the most compact solution possible in an axial direction.
According to an aspect of the invention, a planetary transmission comprises a sun gear, which constitutes an input drive means to the planetary transmission, a ring gear arranged around the sun gear, a planet carrier which is designed to rotate and which carries at least one planet wheel, which planet wheel meshes with the sun gear and the ring gear, the planet carrier constituting an output drive means from the planetary transmission. The planetary transmission further comprises a wet disk brake, a first set of brake disks in the brake being rotationally locked to the planet carrier and thereby in operation rotating at the rotational speed of the planet carrier. The brake further comprises a means for circulation of a cooling fluid through the brake, the brake circulation means being rotationally locked to the sun gear and thereby in operation rotating at the rotational speed of the sun gear. The fact that the sun gear rotates substantially faster than the planet carrier means that an efficient cooling of the brake is achieved. The cooling fluid is forced radially outwards by the brake circulation means.
According to a preferred embodiment said means for circulation of the cooling fluid is arranged, at least substantially, radially directly inside the brake in order to force the cooling fluid outwards to the brake as the cooling fluid rotates under the effect of the centrifugal force. In other words, viewed in a radial direction there is an overlap between the position of said means for circulation of the cooling fluid and the actual brake.
According to a further development of the preceding embodiment said means for circulation of the cooling fluid comprises a plurality of elements for forcing the cooling fluid, and the cooling fluid forcing elements and the brake disks in the first set are arranged so that they alternate in an axial direction. In this way the cooling fluid is forced in between the opposing brake surfaces of the brake designed for engagement with one another. Said means for circulation of the cooling fluid is preferably disk-shaped.
According to a further development of the preceding embodiment said means for circulation of the cooling fluid comprises a third set of brake disks. This creates the prerequisites for a further braking effect. The third set of brake disks is arranged radially inside the engagement surfaces between the first set and a second set of brake disks in the brake. The third set of brake disks is preferably designed to interact with the first set of brake disks.
According to a further development of the preceding embodiment the opposing surfaces of the first and third set of brake disks, which are designed to interact with one another, form a part of a parking brake. The service brake function has thereby been combined with a parking brake function in a compact, space-saving manner. The parking brake preferably comprises a separate brake piston that is suitably spring-loaded.
According to a further preferred embodiment the brake disks in the first set comprise means for rotationally locking the brake disks directly to the planet wheel journal. This creates the prerequisites for a brake having a smaller overall outside diameter than when the brake disks are seated radially outside the planet carrier. In order to be able to carry not only the planet wheel but also a plurality of brake disks, the planet wheel journals have been lengthened in comparison to hitherto known planet wheel journals.
According to a further development of the preceding embodiment each of the brake disks in the first set comprises at least one hole, in which said planet wheel journal is received. This connection entails less machining than when a splined connection is used.